Medical ultrasound imaging and therapeutic systems are rapidly becoming increasingly complex both in terms of their hardware and software. While the resulting increased diagnostic capability and value of such systems are extremely attractive to end-users, system manufacturers must assure that the increased complexity does not result in excessive cost, size, weight, or power requirements. Minimizing these physical characteristics while providing ever increasing capabilities and value has increased the manufacturers needs for the latest in integrated circuit logic and memory devices, as well as for the latest in data-storage devices and compact efficient power supplies. In addition, these same requirements are also increasing the need for the latest in discrete electro-mechanical devices such as discrete switches and relays. Some ultrasound systems contain literally hundreds of such components, particularly in the case of newer systems having as many as 512 channels. Unfortunately, the improvement-rate for these latter discrete electro-mechanical components in terms of their integration, size, cost, efficiency, or reliability has not been as large as the improvement rate for the former above-mentioned components.
In addition, there are numerous performance reasons why today's discrete electro-mechanical devices are becoming unsatisfactory in ultrasound equipment design. Some of these reasons include high on-impedance, low off-impedance, stray capacitance, high insertion losses, high power consumption and poor power-switching capacity.
While electrical switching can be accomplished using electronic devices such as field effect transistors and thyristors, electro-mechanical contactors are preferable in certain applications. One disadvantage of electronic switches results from leakage currents that cause finite current flow in the “OFF” position. On the other hand, electro-mechanical switches have a visible open position; no current flows in the “OFF” position. The isolation in mechanical relays is determined by the contact gap, and this distance can be adjusted to suit the isolation needs of a variety of applications.
Also, in the proximity of high current systems, electronic devices are considerably sensitive to capacitive coupling and electrostatic discharge. Electro-mechanical relays exhibit good electromagnetic compatibility, generally being insensitive to such effects.
Furthermore, today's discrete electro-mechanical devices are also physically inadequate. Ultrasound transducers increasingly need greater multiplexing capability wherein one may have many more piezoelements in the transducer than wires in the transducer cable. The current difficulty associated with such multiplexing (switching of electrical signals from a greater number of piezoelements among a lesser number of connecting wires) is that today's discrete electro-mechanical devices cannot easily be integrated in large numbers on a single IC chip. Therefore, they consume a lot of space, cost, power and weight and are avoided in large numbers, especially when the need is in the transducer or transducer connector itself.
Finally, another disadvantage of electronic switches is in the area of safety. Protective relays should in any situation which occurs, be in a position to switch off and isolate the faulty circuit. Electronic components cannot fulfill this requirement because in case of electrical breakdown or thermal overload, they generally conduct current in both directions, and are no longer able to interrupt. Thus, mechanical relays, instead of semiconductor switches, must be used for functions meant for safety.
Accordingly, there is a need for an ultrasound system for medical imaging or therapy incorporating micro-mechanical devices which retains the benefits of discrete electro-mechanical devices and provides the additional benefits of reduced size, reduced cost, improved signal integrity, reduced power consumption and higher voltage pulsing capability.